1. Field of the Invention
The present invention relates to a novel production method for optical waveguides and gratings and related devices. More particularly, the invention relates to a method of fabricating optical devices including waveguides and gratings using photosensitive polymeric dielectric compositions using electron beam lithography.
2. Description of the Prior Art
Optical devices employing waveguides and/or some type of wavelength selective device such as a grating are of critical importance to the fiber optic telecommunications industry. Optical telecommunications systems employing technologies such as Wavelength Division Multiplexing (WDM) use a variety of wavelength selective optical devices. Lowering the cost of telecommunications systems is a critical factor in delivering more services to customers at a lower cost-per-customer. The cost of installing, upgrading or expanding a fiber optic network system is typically dominated by 2 factors: cost of installation and cost of the fiber optic components. Lowering the cost of fiber optic components could make a significant impact on cost-per-customer of delivering additional telecommunications services.
One factor involved in the cost of manufacturing fiber optic components employing integrated optical elements is the cost of fabricating the actual chip that contains the optical waveguides, gratings, etc. Precise control over the fabrication process is needed and any process for making such devices should be able to be made in high volumes with as few steps as possible. In addition, any manufacturing platform should be versatile enough to allow for many different types of devices to be easily fabricated, enabling a variety of new devices to be developed.
In order to address this need, many processes for fabricating integrated waveguides using many materials have been explored. Silicon On Insulator (SOI) technology has been successfully used to fabricate a variety of waveguides and waveguide devices. In addition, polymer based waveguides have also been explored. One material in particular, which has been considered for use as an optical waveguide, is bisbenzocyclobutene (BCB). This material has been shown to exhibit low optical loss, excellent planarization characteristics and the ability to withstand high optical power densities.
Yet another very important aspect of many optical devices is the active tuning or changing of their optical characteristics by using some controllable optical, electrical, thermal and/or mechanical property. This is particularly critical for telecommunications applications such as dense wavelength division multiplexing (DWDM). More specifically, tunable optical filters for DWDM channel separation/multiplexing or tunable gain flattening filters for optical amplifiers are very important to emerging telecommunications systems. In addition, tunable dispersion compensation gratings are very important for long haul multi-gigabit telecommunications.
Accordingly, it is an object of the present invention to provide a new and improved method of making optical waveguides using dielectric materials.
Another object of the present invention is to provide a method of making optical devices having waveguides and gratings using dielectric materials.
A further object of this invention is to provide a method of making optical devices having waveguides and gratings where the accuracy of the physical dimensions of the gratings is between 5 nm and 50 nm.
A further object of the present invention is to provide a method of making optical devices having waveguides and gratings using dielectric materials and electron beam lithography.
A further object of this invention is to provide optical devices and methods for manufacturing those optical devices whose optical characteristics can be tuned.
Using polymeric dielectric materials (e.g. materials derived from bisbenzocyclobutene monomers) and an electron beam lithography process for patterning this material, we have developed a process for fabricating optical waveguides with complex integrated devices such as gratings. Such gratings are not limited to one-dimensional type gratings but can include 2 dimensional gratings such as curved gratings or photonic crystals. Due to the properties of BCB, this process could also be implemented using optical photolithography depending upon the waveguide dimensions desired and the grating dimensions desired. Alternatively, the optical waveguide could be patterned using optical lithography and the grating can be patterned using electron beam lithography. Gratings with much more dimensional precision can be fabricated using electron beam lithography. Gratings fabricated with precise dimensional control are required, for example, for many applications including Dense Wavelength Division Multiplexing (DWDM) for telecommunications applications. In addition, the general process described below can be applied to the fabrication of complex lightwave circuits containing, for example, multiple optical waveguides, couplers/splitters, grating based filters and even more complex devices and structures. Many other variations on these devices and structures as well as other structures can be developed using this process as would be apparent to anyone skilled in the art.
The present invention discloses various optical devices and a method of producing an optical device having integrated waveguide and grating structures comprising: applying onto a cladding material an energy sensitive composition to produce an first energy sensitive coating on said cladding; patternwise exposing said first energy sensitive coating with an energy source to produce a first coating having exposed and unexposed regions; contacting a developer and said first coating having exposed and unexposed regions to selectively remove said unexposed regions to produce a first patterned layer; curing said first patterned layer to produce a waveguide structure; applying an energy sensitive composition onto said waveguide structure to produce a second energy sensitive coating; patternwise exposing said second energy sensitive coating with an energy source to produce a second coating having exposed and unexposed regions; contacting a developer and said second coating having exposed and unexposed regions to selectively remove said unexposed regions to produce a second patterned layer; and curing said second patterned layer to produce a grating structure thereby producing an optical device having integrated waveguide and grating structures. The energy source is selected form the group consisting of electron beam energy and optical radiation. Cladding material has an index of refraction less than the energy sensitive composition and is perferably spin on glass or silicon dioxide. Cladding material may be first applied to a substrate and may be applied to said substrate by plasma enhanced chemical vapor deposition.
The substrate may be selected form the group consisting of: semiconductors glasses, plastics, polymers, metals, ceramics, insulators, organic materials, inorganic materials, and any combinations thereof. Where the substrate is ceramic, BCB may be applied to the ceramic prior to applying cladding material. Where the energy source is electron beam energy the patterned layers can be nano-scale patterned layers. Where the energy source is optical radiation, the patterned layers can be micro-scale patterned layers.
The energy sensitive composition is selected form the group consisting of: momomers, oligomers, and polymers and any combinations thereof. The energy sensitive composition is a preferably a dielectric composition and preferably a dielectric polymer. The energy sensitive composition of the invention is electron beam or optical radiation curable, organic soluble mixture comprising at least one oligomerized cyclobutarene made from a cyclobutarene monomer bridged by oranopolysiloxane and at least one photosensitive agent in an amount sufficient to convert the mixture to a polymer insoluble in a development solvent upon exposing the mixture to electron beam or optical radition. The oganopolysiloxane of the mixture may be divinyltetramethydisiloxane. The photosensitive agent may be a poly(aryl azide) such as 2,6-bis(4-azidobensylidene)-4-alkylcyclohexanone or 2.6-bis(4-azidobenzylidene)-4-methylcyclohexanone. The mixture may contain an antioxidant derived form 1,2,dihydro-2,2,4-trimethyquinoline. The energy sensitive composition is preferably bisbenzocyclobutene (BCB).
The first energy sensitive coating may be soft baked prior to patterwise exposing this coating with an energy source. Also, the second energy sensitive coating is may be soft baked prior to patterwise exposing this coating with an energy source.
The optical device of the invention may have a plurality of waveguides and a plurality of gratings.
Other features and advantages of the present invention will be apparent from the following detailed description, and from the claims.